A batch is a single production run. That is the whole of the working definition, and it is worth holding onto before the word is asked to mean anything else.
The term has been worn thin by marketing. Two words, repeated on labels until they signal nothing more than a tone, handmade, scarce, worthy of a higher price. The phrase has become a substitute for the thing it once described. Which is a loss, because the thing it described is real, and more interesting than the phrase has ever managed to be.
One run, and what it contains
To make a batch is to commit a measured quantity of materials to a single process at a single time. The oils are weighed. The lye solution is brought to temperature. The two are combined, and from the moment they meet, the run is its own event, bounded and unrepeatable. The next batch will be made from the same recipe. It will not be identical.
This is not failure of method. It is the consequence of working with materials that are themselves not identical.
Olive oil pressed in one year carries a different fatty-acid balance than the next. A coastal studio in October is colder than the same room in June, and temperature governs how quickly oils and lye come to trace, how the bars set, how the surface finishes. The maker’s hand is part of the variable too, the moment a pour is judged ready, the angle of a mould, the few degrees of warmth a vessel holds. None of these can be fully fixed. All of them register in the result.
So one batch sets a fraction firmer. Another carries the scent slightly differently because the season altered the oil it was suspended in. A surface cures to a marginally different sheen. These are not flaws. They are the record of a particular run, made on a particular day, from a particular set of ingredients that existed only then.
What industry removes
Industrial production exists, in large part, to delete this. The entire apparatus of scale, standardised inputs, controlled environments, synthetic substitution, continuous process rather than discrete runs, is built to make the ten-thousandth unit indistinguishable from the first. Variation is the enemy. It is measured, traced, and engineered out until the product is the same everywhere, always.
There is nothing dishonest in that. Consistency at scale is a genuine achievement and it serves a genuine purpose. A person who wants the same thing every time is right to want it, and right to be given it.
But it should be named for what it is: the removal of the very thing a batch carries. When every unit is identical, the concept of a batch has dissolved. What remains is output, a continuous stream from which any given piece is interchangeable with any other. The run no longer exists as a distinct event. There is only the line, running.
A batch is the opposite proposition. It holds that the conditions of making leave a mark, and that the mark is not noise to be filtered but identity to be kept. The bar in hand was made then, from those materials, at that temperature, by that judgment. Its small difference from its neighbour is not a defect tolerated. It is the evidence that something was made rather than produced.
This is what the marketing phrase buried. Not a claim about size, and not a claim about worth. A claim about what variation means, whether it is an error to suppress, or a signature to leave intact.
The honest answer is that it depends entirely on what you are trying to make.